# How does contraction of polyethylene strip depend upon the heat it receives?

Strip is made of polyethylene and is cold drawn so that all polymer chains are oriented in one direction. Now, if heat is supplied to it via external source then how much will this strip contract. Is there a general formula or any article which contains this data for some other similar material?

Answer to a related question detailing why some polymers contract

The change in dimensions of a material because of temperature change is determined by the Thermal expansion coefficient. In case of contraction, it will be a negative number. This coefficient can be defined for changes in volume, area, or length. For your question, length seems to be the preferred choice.

$$\alpha_L = \frac{1}{L}\frac{dL}{dT}$$

Here $$\alpha_L$$ is the coefficient, $$L$$ is length and $$T$$ is temperature.

If $$\alpha_L$$ doesn't change much in the ranges of $$T$$ that you are working in, and neither does $$L$$, the above equation can be simplified to

$$\Delta L = L.\alpha_L\ . \Delta T$$

The value of $$\alpha_L$$ for a material may be found in a list in a material engineering handbook. A quick internet search provided me with these results in $$10^{-6} m/(m K)$$ at $$25ºC$$

Polyethylene (PE) $$= 200$$

Polyethylene (PE) - High Molecular Weight $$= 108$$

If you want to calculate how much $$T$$ will change by the amount of heat energy it receives, you will need to use the material's Heat Capacity